1. Field of the Invention
The invention relates to a dental cap for use as a carrier for the veneer of a jacket crown.
2. Description of the Prior Art
A dental cap is already known of a noble metal foil of substantially cylindrical or cylindrical-frusto-conical shape, which starting from a circular foil piece is formed by folding over the outer region thereof in the direction towards the axis of rotation of the foil piece to form mutual overlappings, the overlapping regions being joined undetachably to each other (see US Pat. No. 4,492,579).
Except for the centre region of the circular foil piece this cap is prefolded in harmonica manner and at the same time folded over in the direction towards the axis of rotation of the foil piece so that the outer region of the cap has an appearance corresponding substantially to a half-opened umbrella. The cap thus formed is then placed by the dental technician on a tooth stump model corresponding to the peculiarities of a patient, pressed in the central region radially against the tooth stump model and held fixed in this manner with simultaneous rolling of the harmonica pleats of the outer region against the outer surface of the tooth stump model, this corresponding substantially to the further closing of an umbrella and wrapping it round the umbrella stick. With a view to exact adaptation of the dental cap to the tooth stump model, the operation of folding the harmonica pleats together and rolling them against the outer surface of the tooth stump model must be carried out very accurately. Also, this work can be done only manually by the dental technician and is thus relatively time-intensive and therefore expensive. In addition the rolling of the foil against the tooth stump model requires great skill on the part of the dental technician to avoid unintentional cross folds or the like resulting in local irregularities in the wall thickness of the cap, which cannot be equalized even on subsequent insertion of the rolled cap into a so-called swager. Such unintentional transverse folds can contain air inclusions which cannot be filled with liquid gold in the subsequent treatment in a flame to obtain an inseparable mutual fixing of overlapping regions of the foil.
With a view to a more rapid and more economical producability starting from the dental cap described above, and in particular to avoid excessive demands on the skill of the operating dental technician, it has elsewhere already been proposed to divide the outer region of the foil piece into at least two wing-shaped flaps, adjacent flaps being connected together at a distance from the centre of the foil piece corresponding to at least half the diameter of the cap upper side. Admittedly, the dental cap formed in this manner can be made economically and simply and indeed without particular skill on the part of the dental technician working it; since, however, the end points of the cuts bordering two adjacent flap sides coincide, i.e. the two cuts terminate at a single point, there is a danger when folding the flaps over that small areas of the dental cap are left open. These open areas, however small they may be, involve the risk that they cannot be satisfactorily sealed on mutual inseparable fixing of the overlapping regions by melting on dusted gold powder or the gold of the foil itself.